Presently, gaseous fuelled internal combustion engines for heavy duty trucks are gaining more recognition for operating efficiently with reduced levels of pollutants in the engine exhaust as compared to diesel or gasoline engines. Generally such engines are fuelled with natural gas, but other combustible gaseous fuels, such as methane, propane, butane, hydrogen, and blends of such fuels can be used. The gaseous fuel for fuelling an internal combustion engine can be stored in tanks either as compressed gas (for example, compressed natural gas (CNG)) or cryogenically in liquefied form (for example, liquefied natural gas (LNG)).
When gaseous fuel is stored in liquefied form, a pump can be used to increase the pressure of the LNG and to pump it from the storage tank into the fuel supply line. Along the fuel supply line, a vaporizer converts the LNG into vapor before supplying it to the engine's combustion chamber. When gaseous fuel is stored in a CNG tank, the pressure within the tank can be lower than the pressure needed to deliver the CNG into the combustion chamber, because the storage pressure drops when fuel is consumed by the engine. Therefore, the pressure of the CNG supplied to the engine has to be increased from the storage pressure to a higher pressure at which it will be injected into the combustion chamber through the fuel injectors. This can be done by a pressure amplifier, a compressor or other fuel pressure increasing device. For the high pressure needed to inject a gaseous fuel into a combustion chamber, pressure increasing devices, such as for example an LNG pump or a CNG pressure amplifier, typically use reciprocating pistons or some other means based on the positive displacement principle and such devices can introduce pressure pulsations into the gaseous fuel stream. If pressure pulsations are carried over to the fuel injectors, this can introduce errors in controlling the actual injected fuel quantity relative to a commanded injected fuel quantity.
During normal operation, there can be times when there are sudden fuel demands that cannot be immediately met by the pump alone and therefore many of the existing engine fuel supply systems comprise an accumulator which temporarily stores an amount of fuel supply at a pressure required for injection into the combustion chamber and makes it readily available to the engine when needed. In its simplest form, an accumulator is a storage tank that is connected to the fuel supply line, and to be effective, the accumulator serves as a reservoir that is sized large enough to reduce pressure fluctuations caused by pulsations generated by the pressure increasing device and by sudden fuel demands that exceed the capacity of the flow rate through the pressure increasing device. However, a disadvantage of gaseous fuel accumulators is that they are large. If not designed specifically for engine applications, they can be relatively expensive and can also require frequent safety inspections.
Gaseous fuel supply systems often require additional components such as filters, which remove impurities from the fuel supplied to the combustion chamber, pressure and/or temperature sensors, which can provide feedback to the control system for regulating the fuel pump strokes, and safety and control devices, such as pressure relief valves. Such components are fluidly connected to the fuel supply line and between each other through multiple plumbing devices (for example, fittings, adaptors) which increase the risk of leaks and therefore diminish the overall reliability of the fuel supply system.
There can also be pressure pulsations introduced into other parts of the fuel system, such as pressure pulsations introduced into the fuel rail that supplies fuel to the fuel injectors, caused by the cyclical actuation of the fuel injectors. Such a problem has been addressed in the prior art, for example in United States Pat. App. Pub. No. US 2002/0043249 A1, which describes a fuel rail comprising several dampening sections, each section comprising two dampening members, disposed opposite each other and offset at a predetermined distance to cause a transverse direction change of the fuel flow which attenuates the pressure pulsations within the fuel rail. Alternatively, the fuel rail can comprise an integrally formed dampening section of a smaller inner diameter than the main portion of the fuel rail. The effect of the reduced cross-section of the rail is to reflect a portion of the pressure waves back into oncoming pressure waves, thereby at least partially cancelling the pressure pulsations produced within the fuel rail. Such arrangements claim to be effective for dampening the relatively low frequency and low amplitude pressure pulsations within the fuel rail caused by the cyclic operation of the fuel injectors, but they do not address the higher frequency pulsations that can be introduced into a fuel supply line by a pressure increasing device.
Other devices are known from the prior art for dampening pressure pulsations generated in gas streams by a piston type compressor whose operation can trigger such pressure waves. As described in British Pat. Nos. 605,054 and 658,562, and in U.S. Pat. No. 2,795,374, such devices generally comprise an elongated housing having at least two separate chambers, one communicating with the gas inlet and the other communicating with the gas outlet and a pipe of a greater length than that of the elongated housing, the pipe forming an elongated passage fluidly connecting the at least two chambers. When gas flows through the relatively restricted and elongated passage formed by the pipe, the pressure pulsations within the gas stream are dampened. However, such devices for dampening pressure pulsations require additional elements, as described above, which add to their constructional complexity.
Therefore there is a need for a simple, more compact, cheaper module for dampening the pressure pulsations of a relatively medium frequency generated by a pressure increasing device installed in the gaseous fuel supply system of a gaseous fuelled internal combustion engine system and for managing flow therethrough.